To think one could make such a fuss over the palette of a game we've been seeing screen shots of for years is itself curious. It brings back ugly memories of fanboys crying, "Celda!' ... except inverted. Instead of being too colorful, now it's not colorful enough. But complaining about the game's decidedly earth-tone infused aesthetic is akin to criticizing Schindler's List for being black and white ... you're welcome to that opinion, but it's an entirely subjective one devoid of any artistic allowance.
And the engine? Yeah, it's a Gamecube game. It's a Gamecube game running on hardware that is (especially in this case) a Gamecube. If we're going to be criticizing the game for not being made on another platform with superior hardware, then why wasn't Super Mario Bros. made for Super Nintendo ... those graphics were weak, amirite? Why wasn't Gears of War made for Xbox 720 ... it should totally be in virtual reality!